The capacities of batteries in battery-based uninterruptible power supplies (UPSs) vary depending on several factors, including temperature, age, and load. As the batteries age, they are preferably replaced once their capacities drop below desired capacities (e.g., runtimes). Preferably, the batteries are replaced before their diminished capacities affect desired operation of the UPSs, e.g., by relying on a battery with an undesirably-low runtime such that the UPS is unable to provide backup power to a load for a desired amount of time. To determine when a battery's capacity has diminished more than desired before being relied on to power a load, periodic testing may be performed on the battery.
Previously, determining a UPS's battery capacity has involved powering a load with the battery to significantly or fully discharge the battery to determine the battery's capacity. This can take a long time (e.g., 4 hours) and when the battery is significantly or completely depleted, the UPS cannot provide desired/adequate backup power. Often times, this kind of depletion testing is infrequently performed and leads to reporting that a battery needs replacing long after the capacity has degraded to unacceptable levels. In power supplies such as UPS's, this is not acceptable. Previously, deciding when the battery should be considered for replacement or should be discharge tested to verify its actual capacity has been made based primarily or solely on battery age, which ignores other factors affecting age and may lead to either premature or late battery replacement.